For the improvement of material properties of metallic component parts, it is known that one may influence their material microstructure using heat treatment methods. Steels are particularly suitable for such treatment methods, in addition to a great multitude of metals, and of the steels, for instance, 100Cr6 reacts well to treatment using such austempering methods.
With regard to 100Cr6, heating of the material is first carried out to a temperature of approximately 850° C., for example, so that a so-called austenitic structure is formed in the material. The component parts thus heated must subsequently be rapidly quenched to the austempering temperature. A temperature range of ca. 220° C. is preferred for this, at which the so-called bainitic structure comes about. However, this temperature is only slightly above the so-called martensite start temperature, to which the work pieces absolutely must not cool off during the microstructural transformation process, since this would result in massive interference in the desired, and particularly advantageous, bainitic structure.
To this end, an installation is described in German Published Patent Application No. 100 44 362, in which the components that are to be heat-treated, which are also designated as semi-finished products, are moved in a heated transport car after quenching and regulated catching at transformation temperature, and are transported in the transport car to an annealing furnace.
To do this, the components are taken out of the quenching chamber that is under excess gas pressure [pressure above atmospheric pressure] during the conversion, and are transported, using a transport car, to the transformation chamber that is situated downstream in the process flow, are placed in it and held in it at constant temperature.
When the component parts are moved out of the quenching chamber there is a danger, on the one hand, that, because of a surrounding gas temperature that is too low, the outer areas of the component parts, especially thin-walled sections of the component parts, are cooled too severely. Therefore, it may not be excluded that the gas temperature briefly falls below the martensite start temperature, and thereby at least endangers, if not even prevents, the microstructural development of bainite, for instance, in the component parts. This happens because the edge regions of a component part very rapidly take up the gas temperature, especially in thin-walled places, at corners or at courses of thread.
On the other hand, there is the danger that, during the course of the conversion setting in due to the microstructural transformation in the components, an inadmissible increase in the component temperature occurs, caused by the exothermic processes brought about in this instance, which will also cause massive interference in the transformation of the material microstructure because of microstructural transformation, setting in as a result, into perlite and/or continuous bainite.